Self-similar growth dynamics of lipid droplets in live cells

Lipid droplets are cellular organelles consisting of a hydrophobic lipid core enclosed by a monolayer of phospholipids. Formation of lipid droplets is an important step in cell metabolism. Lipid droplets start forming as a result of accumulation of neutral lipids, mostly triacylglycerols (TGs), in the endoplasmic reticulum. Experimental studies indicate that growth of lipid droplets slows down dramatically when they reach a certain size, even when the synthesis of TGs continues at the same rate. We propose a model that explains this phenomenon quantitatively by accounting for the effect of lipolysis at the lipid droplet surface and determine the limiting size of the droplet. One of the predictions of the model is that the radius versus time curves are self-similar, i.e. that data under different experimental conditions should fall onto a single universal curve in appropriate nondimensional coordinates. We verify that this is indeed the case for the available experimental data from live cells studies. The role of new lipid droplet formation in overall dynamics of the previously formed ones is also discussed.